Contactless communication device and user device including the same

1. A contactless communication device, comprising: a field strength detecting circuit configured to detect a strength of a field induced on an antenna; a card circuit configured to demodulate a signal received via the antenna during a reception interval of a card mode; a processing unit configured to process the demodulated signal; and a reader circuit configured to transmit modulated data via the antenna during a transmission interval of the card mode, the modulated data being modulated from data provided from the processing unit after processing the demodulated signal, wherein the device is configured to adjust an output power of the reader circuit according to the field strength detected.

2. The contactless communication device of claim 1 , wherein the transmitted modulated data is responsive to the received signal.

3. The contactless communication device of claim 1 , wherein the device is configured to adjust the output power of the reader circuit according to the field strength detected before the transmission interval of the card mode, and to maintain the adjusted output power during the transmission interval of the card mode.

4. The contactless communication device of claim 1 , wherein the output power of the reader circuit is adjusted according to the field strength detected before the transmission interval of the card mode, and the adjusted output power is adjusted according to the field strength detected during the transmission interval of the card mode.

5. The contactless communication device of claim 1 , further comprising: a clock recovery circuit configured to generate a clock signal based on a carrier of a field induced on the antenna.

6. The contactless communication device of claim 5 , wherein the clock recovery circuit is configured to perform a course tuning on a frequency of the clock signal during an operating interval of the processing unit, and to perform a fine tuning on the frequency of the clock signal during the transmission interval of the card mode.

7. The contactless communication device of claim 5 , wherein the device is further configured to supply the clock signal to the reader circuit with the data during the transmission interval of the card mode, and the reader circuit is configured to drive the antenna with the adjusted output power in response to the clock signal and the data.

8. The contactless communication device of claim 1 , wherein the card circuit does not provide a modulation function.

9. The contactless communication device of claim 1 , wherein the card circuit provides a modulation function and a demodulation function.

10. The contactless communication device of claim 9 , wherein the processing unit is configured to activate the modulation function of the card circuit when communication using the reader circuit has failed.

11. A user device, comprising: an NFC transceiver; and an antenna impedance matching network connected to the NFC transceiver, wherein the NFC transceiver comprises: a field strength detecting circuit configured to detect a strength of a field induced on an antenna of the antenna impedance matching network; a first circuit powered by an external signal, the first circuit configured to demodulate a signal received via the antenna during a reception interval of a card mode; a processing unit configured to process the demodulated signal; and a second circuit powered by the user device, the second circuit configured to transmit data provided from the processing unit via the antenna during a transmission interval of the card mode, wherein the user device is configured to adjust an output power of the second circuit according to the field strength detected.

12. The user device of claim 11 , wherein the user device is configured to adjust the output power of the second circuit according to the field strength detected before the transmission interval of the card mode, and to maintain the adjusted output power during the transmission interval of the card mode.

13. The user device of claim 11 , wherein the user device is configured to adjust the output power of the second circuit according to the field strength detected before the transmission interval of the card mode, and to further adjust the adjusted output power according to the field strength detected during the transmission interval of the card mode.

14. The user device of claim 11 , wherein the user device is configured to adjust the output power of the second circuit according to the field strength detected during the transmission interval of the card mode.

15. The user device of claim 11 , wherein the NFC transceiver further comprises a clock recovery circuit configured to generate a clock signal based on a carrier of a field induced on the antenna.

16. The user device of claim 15 , wherein the clock recovery circuit is configured to perform a coarse tuning on a frequency of the clock signal during an operating interval of the processing unit and perform a fine tuning on the frequency of the clock signal during the transmission interval of the card mode.

17. The user device of claim 15 , wherein the user device is further configured to supply the clock signal to the second circuit with the data during the transmission interval of the card mode, and the second circuit is configured to drive the antenna with the adjusted output power in response to the clock signal and the data.

18. An operating method of a contactless communication device which includes a reader circuit and a card circuit connected to an antenna impedance matching network, the method comprising: detecting a strength of a field induced on an antenna; demodulating a signal received via the antenna; processing the demodulated signal; and modulating the processed signal, wherein the demodulating is performed via the card circuit, the modulating is performed via the reader circuit, and an output power of the reader circuit is adjusted according to the detected field strength.

19. The operating method of claim 18 , further comprising: generating a clock signal based on a carrier of a field induced on the antenna; using the clock signal for modulation of the processed signal; and performing coarse tuning of the clock signal during a processing interval of the demodulated signal; and performing fine tuning of the clock signal during a transmission interval of a card mode.

20. The operating method of claim 18 , wherein an output power of the reader circuit is adjusted according to the field strength detected before a transmission interval of a card mode, and the adjusted output power is maintained in the transmission interval of the card mode or is further adjusted according to the field strength detected in the transmission interval of the card mode.

21. A near field communication device, comprising: a receiving circuit configured to receive and demodulate a first signal received at an antenna of the near field communication device from outside the near field communication device; and a transmitting circuit configured to modulate and transmit a second signal from the near field communication device, in response to the first signal, wherein: the near field communication device is configured to detect a field strength of the first signal, and to control an output power for the second signal based on the detected field strength.

22. The near field communication device of claim 21 , further comprising: a processor configured to control the output power for the second signal.

23. The near field communication device of claim 22 , further comprising: at least a first output driver, wherein the processor is configured to control the output power of the first output driver based on the detected field strength.

24. The near field communication device of claim 23 , further comprising: at least a second output driver, wherein the processor is configured to control the output power of the first output driver and the second output driver based on the detected field strength.

25. The near field communication device of claim 24 , further configured to: modulate load by alternatively driving first and second chip terminals respectively connected to the first and second output drivers.

26. The near field communication device of claim 21 , further comprising: a processor configured to: activate the receiving circuit and deactivate the transmitting circuit during a reception interval; and activate the transmitting circuit and deactivate the receiving circuit during a transmission interval that follows the reception interval.

27. The near field communication device of claim 26 , wherein: the processor is further configured to adjust the output power for the transmitting circuit prior to the transmission interval.

28. A method of performing near field communications, the method comprising: receiving and demodulating a first signal received at an antenna of a device; detecting a strength of an RF field at the antenna; processing the demodulated signal; modulating the processed signal; and transmitting from the device a second signal that reflects the modulated processed signal, wherein: an output power for the second signal is adjusted according to the detected field strength.

29. The method of claim 28 , wherein: demodulating the first signal is performed by a card circuit of the device; and modulating the first signal is performed by a reader circuit of the device.

30. The method of claim 29 , further comprising: activating the card circuit and deactivating the reader circuit during a reception interval; and deactivating the card circuit and activating the reader circuit during a transmission interval that follows the reception interval.